1. Field of the Invention
This invention concerns systems for the assessment of the influence of variations in temperature on perishable products, and in particular concerns a residual lifetime indicator device for consumer products, including food products.
2. Description of the Related Art
The majority of industrial products, and in particular the products of the food and agricultural and pharmaceutical industry, have properties which perish, until they reach zero, within a given time period, which is generally shown as the validity or expiry date of the product. It should however be stated that generally, as is often stated on the packs of the products, this date refers to the intact product stored in an optimal manner; however it is not always possible for the consumer to establish whether the product has been stored in the most appropriate way before its purchase.
From U.S. Pat. No. 5,531,180, a device is known which is capable of recording the temperature variation which a product, in particular a deep-frozen product, has undergone, and to indicate its extent by suitable means. However, this device does not provide any assessment as to the remaining effective life of the product, and thus the information it records is difficult to communicate to and understand by the consumer, who normally has neither the knowledge nor the technical means to carry out assessments of this type.
In WO 99/044021, a time-temperature indicator is described wherein a small bar of a given material is subjected to a traction load, for example from a spring, and the given material is capable of varying its response to the traction depending on the temperature. In this way, by appropriately selecting the stretchable material and the means for subjecting it to a traction load, it is possible to obtain a device which provides information concerning the residual lifetime of the product to which the device was linked. However, with regard to practical application, this type of solution presents a series of difficulties connected mainly to the selection of the materials in question; in the first place, considerable difficulties in calibrating the indicator can also arise. Moreover, many of the materials can turn out to be toxic or at any rate noxious, and poorly suited to a device intended for use on food or pharmaceutical products. Finally, this device exhibits substantial complications in order to obtain an irreversible indication of the residual lifetime of the product.